O2 sensors are used in the exhaust systems of internal combustion engines and provide information regarding the ratio of air to fuel being supplied to the engine. In general, internal combustion engines need a specific air-to-fuel ratio (or ratio range) to operate correctly. When the ratio is less than desired, not all fuel in the air-fuel mixture is burned or combusted. This situation is referred to as a rich mixture or rich condition and has a negative impact on exhaust emissions. When the air-fuel ratio is higher than desired, excess oxygen is present in the air-fuel mixture. This situation is referred to as a lean mixture or lean condition. When an engine burns lean, engine performance may decrease and, in some cases, may cause engine damage and have a negative impact on exhaust emissions.
Over time, contaminants (such as soot) build up on O2 sensors. If these contaminants are not removed, the sensors will not operate properly. One way to remove the contaminants is to heat the sensor (using an electric heating element contained within the sensor) so that the contaminants are burned off. However, overheating the sensor to burn off contaminants can damage the sensor.